The substitution of pulverized coal for coke in an iron-making blast furnace is well known in the art. Efficient operation of the blast furnace requires that the coal be uniformly distributed in the furnace to prevent channeling of the blast air, as well as other problems. The coal is, normally, injected into the tuyeres which communicate with the furnace. The tuyeres are also used for supplying the high temperature blast air which supports the iron-making reduction of the ore. The tuyeres are generally arranged equiangularly circumferentially around the furnace above the hearth and, consequently, the injected coal is similarly injected at equiangularly located positions around the furnace.
The coal which is injected into the furnace through the tuyeres is, generally, finely ground or pulverized and has a very low, on the order of about 0.5%, moisture. Due to the fine grind of the coal, it is generally transported to the tuyeres by means of a pneumatic system conveying the coal through a system of pipes from the coal preparation facility to the blast furnace. In order to simplify the numbers and the complexity of the pipe system, it is preferred that the ground coal be transported to a coal distributor located adjacent the furnace. The coal distributor preferably provides a suitable number of outlets communicating with the tuyeres. Ideally, the coal distributor should be constructed so that each of the lines feeding a tuyere receives an air/coal suspension of a quantity substantially equal to the amount received by the other lines feeding the other tuyeres. In this way, uniform distribution of the pulverized coal in the furnace can be assured with the result that efficient operation of the blast furnace can be maintained.
Matthys, et al, U.S. Pat. No. 3,204,942, discloses a distributor for pneumatically transporting particulate material, preferably coal. Matthys discloses an upstanding cylinder having a centrally located inlet coal/air supply line and a plurality of equiangularly disposed outlets positioned on a common horizontal plane. The distributor of Matthys discloses an inverted cone disposed in the bottom of the cylinder and having a downwardly diminishing diameter in order to prevent coal accumulation. Experience has shown, however, that the Matthys distributor results in unequal distribution of the coal/air suspension to the lines communicating with the tuyeres. Consequently, the Matthys distributor is not capable of providing sufficient uniformity of coal distribution which would permit greater efficiency in the operation of the blast furnace. While Matthys discloses that flow restrictors may be placed in the lines to effect equality of pressure drop, the actual use of such restrictors has proven to be extremly complicated and that the insertion of one restrictor has an effect on other lines in the system.
Wennerstrom, U.S. Pat. No. 4,027,920, discloses a distributor similar to Matthys' and in which a hollow cylinder is suspended in the distributor aligned with the central opening in order to maintain central orientation of the oncoming stream. Wennerstrom, the assignee of which is also the assignee of the Matthys patent, in commenting on the Matthys patent states "Recent experience has shown the deviation of the incoming stream from its central orientation results in pulsation and non-uniform distribution of the effluent streams." Consequently, there is an appreciation in Wennerstrom by the owner of the Matthys' patent that the Matthys' distributor does not provide optimum distribution to each of the tuyeres. Unfortunately, experience has also shown that the Wennerstrom solution to the Matthys problem results in a similarly non-uniform distribution to each of the tuyere lines.
The present invention discloses a method for controlling the substantially uniform distribution of the coal/air suspension from a multi-outlet distributor which is in communication with the tuyeres of a blast furnace. The method of the invention permits the blast furnace operator to select that level of distributor deviation which can either be tolerated by the blast furnace or which is the best obtainable in view of practical physical limitations. The present method permits a blast furnace operator to contstruct a distributor bottle taking into account the velocity of the coal particles and the diameter of the bottle as well as the distance from the top plane of the cone to a plane coincident with the central axes of the outlet tuyere pipes. Consequently, the present method permits the construction of a distributor bottle in which the distributor deviation may be controlled from zero deviation to that amount of deviation which the furnace operator is willing to tolerate. The present method provides, therefore, a novel and unique means for controlling the distribution of coal to a blast furnace in order to premit optimum efficient operation of the furnace.